Alloys for indirectly-heated cathodes



Oct. 15, 1957 A. M. BOUNDS ALLOYS FOR INDIRECTLYHEATED- CATHODES Filed NOV. 15, 1955 8 Sheets-Sheet I00 HOURS Ef- (volts) Ef- (volts) Ef- (volts) Oct. 15, 1957 A, M. BOUNDS 2,809,890

ALLOYS FOR INDIRECTLY-HEATED CATHODES Filed NOV. 15, 1955 8 Sheets-Sheet 2 l l l 25 50 I00 200 350 500 Hours of Life 9 1 IL 1 l I 0 25 50 .IOO 200 350 500 Hours of Life Oct. 15, 1957 A. M. BQUNDS ALLOYS FOR INDIRECTLY-I-IEATED CATHODESI 8 Sheets-Sheet 5 Filed Nov. 15, 1955 I000 I250 I500 550 26002250 2500 Hours of Life Hours of Life Hours of Li fe Oct. 15, 1957 A. M. SOUNDS 2,809,890

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Unite States Patent 9 2,809,890 ALLOYS For: lNDmECTLY-HEATED oarnonns Ardrey M.;Bounds, Laverock, Pa., assignor to Superior Tube Company, Norristown, Pa., a corporation of Pennsylvania Application November 15, 1955, Serial No. 546,963 18 Claims. (Cl.'75'-170) This invention relates to cathodes for electron tubes, and particularly relates to cathodes of the indirectlyheated type as distinguished from those of the directlyheated or filamentary type.

This application is in part a continuation of my copending application Serial No. 259,505, filed December 1, 1951, now abandoned.

The present invention is in the nature of an improvement upon that disclosed in my Patent 2,566,115. As set forth therein, the inclusion in the base nickel cathode alloy of a small percentage of aluminum within specified narrow limits is effective to shorten the initial activation period of the cathode, to increase the electron emission from the cathode at the same or lower operating temperature, to increase the effective cathode life, and to insure permanency and negligible electrical resistance of the mechanical bond between the cathode base element and its oxide coating of alkaline earth metals.

As originallydisclosed .in my aforesaid application Serial No. 259,505, allot-these desirable cathode chara'cteristics are retained, with. enhancement of some of them, and in addition there is obtained greatly increased ability of the heated cathode to resist deformation under conditions of severe mechanical shock by inclusion in the aluminum-nickel alloy of tungsten Within hereinafter specified narrow percentage limits.

Further and more specifically, the aluminum-tungstennickel alloys embrace d by the present invention as'suited for attainment, in indirectly-heated cathodes, of both greatly enhanced strength at high temperatures and high emission characteristics contain from about 0.5% to tungsten and from about 0.01% to 0.25% aluminum. For obtaining the highest mechanical strength consistent with workability of the cathode alloy stock and for concurrence of superior emission characteristics, the optimum percentage of tungsten is about 4%. For obtaining the best emission characteristics concurrently with superior mechanical strength, the optimum percentage of tungsten is about 2%. In both cases, the preferred narrow range of aluminum is from about 0.05% to 0.1%.

In the following more detailed disclosure of the invention, reference is made to the accompanying Figures 1 to 23 of the drawings in which Figs. 1 to 21 show test curves, below specifically identified, of four cathode alloys, one of which is a tungsten-aluminum-nickel alloy embraced by the invention: More particularly;

Figs. 1 to 3 show curves of emission current vs. cathode-heater voltage;

Figs. 4 to 9 show curves of emission figure of merit vs. cathode life;

Figs. 10 to 12 show curves of emission at normal heater voltage vs. life;

Figs. 13 to 15 show curves of emission at subnormal heater voltage vs. life;

Figs. 16 to 18 show curves of cathode-coating temperature vs. life;

Figs. 19 to 21 show curves of low field emission vs. life; i

ing greater impairment of tube performance. tive component of the interface impedance is damaging,

2,809,890 Patented Oct. 15,1957

Fig. 22 shows the curves of emission 'figure'of merit vs. cathode life for five additional alloys within narrow preferred limits of tungsten and aluminum; and

Fig. 23 shows curves of emission figure of merit vs. cathode life for aluminumtungsten-nickel alloys with excessive aluminum. V

In general, indirectly-heated cathodes .consist of a nickel alloybase element such as a sleeve or cup, having thereon a thin coating of alkaline earth metals such as barium, strontium and the like. After assembly of the cathode and other electrodes within an envelope to form an electronic tube, the cathode is activated by temporarily heating it to substantially above its normal operating temperature. During activation there are reactions between the base and coating materials which convert the coating to a combination of complex oxides of these materials. effective life of the its electron emission heater current.

Using coated cathodeshaving the usual pn'or nickel alloy sleeves, the effective life of high-voltage rectifier tubes in particular has often abruptly terminated far short of normal life expectancy because of eruptive flaking or peeling of the cathode coating. Also, the operation of amplifier, mixer and oscillator tubes has been adversely affected by formation of a high impedance interface between the cathode sleeve, or equivalent, and its coating. The electrical impedance of such interface further increases with age of the tube with correspond- The resis- In subsequent use of the tube, the cathode normally terminates when particularly under cut-off -operation, at,ordinary fre-. quencies: the capacitive component of the interface impedance is particularly damaging at high frequencies even when the tube is not operating .under cut-off condition. 1

Such prior cathodes were also unduly sensitive .to reduced heater voltage so that under conditions of fiuctuating line voltage or of low available voltage, as often encountered in fieldoperations, the operation of the tubes was unsatisfactory. Furthermore, when such tubes were subjected to severe mechanical shock, due for example to the extremely high accelerations encountered in mis-.

sile equipment, they were often rendered inoperative before performing their intended purpose because of buckling or deformation of the cathode with resultant internal short-circuit or significant change of. interelec-.

trode spacing, resulting in substantial changes in electrical characteristics. Bowing also occurred when during the activating period, cathodes of usual nickel alloy sleeves were heated to high temperature in efforts to shorten the activation period.

As shown by test curves later discussed, these shortcomings and disadvantages are overcome by using indirectly heated cathodes made .of a nickel alloy including aluminum (Al) and tungsten (W) within narrow limits of specified low percentages. In tabular form, the broadest range of percentage composition suitable for attainment of these electrical and is shown in the following table.

TABLE I Base:

Co 1% max. Major activating:

W 0.55%. Minor activating:

Mn V 0.15% max.

Si 0.25% max.

is definitely subnormal at normal mechanical properties All of the beneficial effects of aluminum and tungsten within the ranges above specified obtain if the cathode alloy also includes as minor activating agents a small percentage of magnesium (Mg) or silicon (Si), or both. A range of 0.01% to 0.25% is suitable for silicon: a range of'0.01% to 0.15% is suitablefor magnesium: the combined percentage range of both is 0.03% to 0.4% within the above specified maximum limits of. 0.15% magnesium, 0.25% silicon. Impurities or residuals, such ascopper, iron, carbon, sulphur. and titanium, should not be present in'percentages higher than specified in Table I above. Cobalt, usually present with nickel, appears'to have no particular effect upon the emissive, hot strength and-life properties of the cathode unlesspresent in quantity greater than 1%.

Although tungsten itself was previously considered a poor cathode activatingmaterial, in combination with aluminum within the range specified, it has been found by me to have a beneficial effect upon emission. This has been explained by the fact that Ba3WOs,.Ba2TiO4 and 13328104 all react with aluminum to produce BaAlzOa and to free barium, in accordance with reactions of the type and (2) BazTiO(s)+2Al(l)= BaAl2O4'(s) +Ti(s) +Ba(g) The hot strength of indirectly-heated cathodes improves progressively with addition of tungsten but for percentages appreciably in excess of about 5%, the higher cost is without compensatory improvement in emission characteristics. Also for such higher percentages of tungsten, there arise. difiiculties in working the alloy stock to form the metal sleeves, or equivalent cathode elements, by punching, stamping or like metal-working steps. The problems encountered in workability of the. cathode stock are very severe since, for example, seamless cathodes are made with external diameters as' small as .010 inch withv awall thickness of. 0.0015 inch: lockseam, lap-seamtand buttseam cathodes are made as small. as 0.020 outer diameter and 0.002 wall thickness.

For highest hot-strength consistent with workability and enhanced emissionv properties, the optimum percentage of' tungsten in the tungsten-aluminum-nickel alloy is about 4%: for this percentage, electronic tubes subjected to shock levels of 1000 g do not suffer cathode bowing. For highest emissive properties and substantially enhanced hot-strength, the optimum percentage of tungsten in the ternary alloy is about 2%.

The optimum percentage of aluminum in the ternary alloy is from about 0.05% to 0.1%. With less aluminum, its beneficial efiects are insubstantial-.2 percentages of aluminum much above 0.2% are unsatisfactory in one or more respects. Specifically; for upwards of 0.25% aluminum, although the cathode sleeves activate rapidly and initially have high. emission,..their life isrelatively short. Furthermore, for upwardsof 0.25-% aluminum, it is difiicult to fabricate lockseam cathodes and seamless cathodes. of small. diameter because edge cracking and flaking of the metal stock. precludes use. of the cathodes in electron tubes.

As a specific. example of analloy withinthe-limits of Table 1, reference is made toalloy X. of. Table 11 below:

TABLE 11 C2 X C; (Inco Cl Essentially Remainder- The superior characteristics of alloy X for indirectlyheated cathodes as compared with the characteristics of tungsten-nickel, aluminum-nickel and normal cathode alloys C1 to C3 of Table II and as evaluated by use of the ASTM standard diode structure are shown by (1) Figs. 1-3: curves of emission current vs. heater voltage at initial and end-of-life periods;

(2) Figs. 4-9: emission figure of merit vs. life;

(3) Figs. 10I5: emission at specified heater voltages during life;

(4) Figs. 16-18: cathode coating temperature vs. life;

(5) Figs. 1921: low field emission during life;

(6-) Table 111; percent AIS (7) Table IV: dome deposit formation.

These seven evaluation factors are'discussed below under similarly numbered paragraphs.

(1) Figs. 1 to 3 show the relative merit of the alloys of Table II in regard to maximum emission and in sustaining emission'at'reduced or subnormal cathode temperature. The emission current was measured with 40 volts (D. C.) applied to the anodeand with from 2.5 to 6-V0lts (in O.5 volt increments) applied to the cathode heater; At the: initial period of life hours), the emission of the tungsten-aluminum-nickel (X) cathode was higher than the others especially at heater voltages above 4.5. Atthe 2,000-hour life period, the tungstenaluminum-nick'el (X) cathode maintained higher emission levels throughout the entire ra-ngeof heater voltages.

(2) The rate of activation is determined by the level and time for the D. C. emission figures of merit (lsFM) to reach a maximum value. D. C. life is evaluated by the variation or"- the figure of merit throughout life; the activation and'early life (500 hours) of the alloys of Table II are shown in Figs. 4 to 6, and their complete life curves are shown in Figs. 7 to 9. In one life test (Fig; 4), the tungsten-aluminum-nickel (X) cathode activatedto a higher degree than thetungsten-nickel cathode as did the normal cathode of alloy C2. In the two other tests (Figs. 5-6), thetime for activation was about the same for all alloys of Table I-I.' Inone of these tests (Fig. 6), the tungsten-aluminum-nickel (X) attained the highest level: in the other tests (Fig. 5), the tungstenaluminum-nickel (X) was again higher than tungstennickel but lower than aluminum-nickel. In all complete life tests (Figs; 7 to 9), the tungsten-aluminum nickel (X) cathode had, after stabilization, the highest and most uniform level of figure of merit.

(3) As shown in Figs. 10- to 12, all alloys of Table I1 reach their maximum emission levels at approximately the same time for normal heater voltage (6.5 volts). However, the tungsten-aluminum-nickel (X) cathode attained the highest level in all tests and maintained the higher level throughoutli'fe". The relation between the other alloys of Table II differed for the different tests. As shown by Figs. 13 to 15-, the tungsten-aluminumnickel (X) cathode also had the highest and most stable level of emission throughout life at subn'ormal heater voltage (4.5 volts). The relation between the 'other alloys of Table 11 differed for different tests: specifically, in two of them (Figs. 13, 14), the emission of the nor to say, the tungsten-aluminum-nickel alloy shows lower,

thermal losses than the other alloys. Thus at the standardized reduced voltage test point of 4.5 heater voltage, the alloy (X) cathode still operates space-charge limited, whereas the other alloys operate temperature-limited.

() In two of the tests for low field emission, the

heater and anode voltages were 1.75 and 4 volts: in the third tests, the heater voltage was 2 volts and the anode voltage was 5 volts. This change in voltages was in effort to reduce emission variations. The emission under the voltage conditions specified is temperature-limited and therefore sensitive to any change in cathode temperature. The variation in emission current noted throughout these tests is believed due to cathode temperature changes occasioned by variations in physical contact of the heater, cathode and interelectrode'micas. Despite these unconeach'test to show any deposit of sublimed metal, and after 3,000 hours of operation there was only a trace of dome deposit formation Whereas by that time the diodes using the other cathodes of Table II had heavy sublimed metal deposits. These tests show that tubes using tungsten-aluminum-nickel cathodes will have longer life, so far as interelectrode leakage is concerned, than similar tubes using cathodes of the other alloys of Table II.

TABLE IV Rate of dome deposit formation TEST 1 Hours for deposit to form 100 50 0. Diameter and density at end of life trace... 4mm. 6mm. (3,000 hours). heavy. heavy. MM TEST 2 h X G2 I C1 C3 7 Hours for deposit to form 1.750 1,000.--. 0 0.

Diameter and density at very faint faint 7mm. 6mm.

end of life (3,000 hours). trace. trace. heavy. heavy.

trollable variations, the low field emission level for the 95 tungsten-aluminum-nickel (X) cathode was definitely better than the others for one of these tests (Fig. 19).

(6) Percent Me is the change in emission that occurs when the heater voltage is reduced from 6.5 volts to 5.5 volts. It is a measure of the ability of the cathode to maintain uniform emission current corresponding with changes of heater voltage of magnitude commonly experienced with changes in load of power supply lines. In the test of Table III below, the tungsten-aluminumnickel (X) cathode is shown to have the least change in emission by end of life and therefore is more stable than the other cathodes of Table II; 1. e., the cathode having the lowest percent Me is the superior cathode.

TABLE III tests of the foregoing character for determining such effect have been made on a large number of tungstenaluminum-nickel alloys. The alloys testedincludedalloys within a high-tungsten, high-altnninum range of 4 to 5% tungsten and 0.15 to 0.25% aluminum; the mediumtungsten, medium-aluminum range of 1.75% to 2.5% tungsten and 0.07 to 0.15% aluminum; and the lowtungsten, low-aluminum range of less than 1% tungsten and less than 0.07% aluminum. Alloys X1 to X5 of Table Alloy zi g 32 2? figf tgt 4 Vand alloy of Table II above are exemplary of those 100 2,000 3.000 1 tungsten-alummum-mckel alloys which have been found .ours Ours to define, within the limits of Table I, still narrower limits of-aluminurn and tungsten which are best suited for in- 3;$10 1% I: {33 gig directly-heated cathodes considering all of the many faco, of Table II 1.36 5 I 573 tOIS'mVOIVEd. Of these, alloy X4 of Table V below has been selected 'for extensive commercial production.

TABLE V Alloy Base Alloy Major Ao Minor AC7. Residual i 'tivating' tivating N1 oo Al'W Mg $1 on Fe 0 T1 l Remainder.

(7 As shown by Table IV below, the sublimation rate of tungsten-aluminum-nickel (X) cathodes is extremely low despite the fact they are characterized by T the highest operating temperature. It was .the last in 7,

As shown by the curves of Fig. 22 and as indicated in TableVI, all of the tungsten-aluminum-nickel alloys of Table V activate rapidly and retain their characteristic of high emission throughout along life.

in practically all cases, found unsuitable forcommercially useful indirectly-heated cathodes,

TABLE VI Characteristics X1 X1 X; X4 X First sign of dome deposit. none hr 350 hr... one"... 25 hr. Type and diameter at deposit none (1,000 hr.) heavy, 5 mm.... trace; 1 mm.. none (750 hr.-).- heavy, 2 mm. Activation Rate (time to reach stability): I

Lat 6.5 v. (E;)... 25111; 25111:- 5hr. 25hr. 1. FM 100 hr hr 100 hr- 50 hr. 25 hr. Max emission level and time: 7

I. at 6.5 v. (Er) 64 51349.. (100 63.6 Ma. (50 hr.) 64.1 Ma. (100 64g l\)/ia. (200 63g (100 r. r. r. r. I. at 4.5 v. (E1) z: $1348.- (100 00.6 Ma. (50 hr.) 61i'171\)1a'.. (100 60.9 Ma. (25-111.). 60.8 Ma. (50 hr.)

1'. r. 7 I FM 15.4 (100 hr.)-..- 16.1 (50 hr.) 15.8 (100 hr.) 16.3 (350 hr.) 15.8 (25 hr.). D. 0. life emission:

I. at 6.5 v. (Er) 62$ 134a. (1,000 625 l\)/Ia. (1,000 62? 1311a: (1,000 62.7Ma. (750 6331a. (1,000

r.. r.. r.. r.. I. at 4.5 v. (E i) 59.6 Ma. (1,000 58.1 Ma. (1,000 59.2 Ma. (1,000 57.2 Ma. (750" 56.2 Ma. (1,000

hr.). 11r.). hr.). hr.). hr.). I FM 15.7 13.8. Cathode Coating Temperature: 7.5 816 0. (1,000 834 C. (1,000 810 C. (1 000 854 C. (750 hr.) 767 (3. (1,000 hit). r.). hr.). hr.). Heater-Cathode Leakage 6.3 V. (Er) 0 100 v. (Ebk) Diode Analysis:

Interface Color- (betore life) A. (after life) A. Coating Texture (afterlife) M. Coating Hardness (after life) 8+. Coating adherence Good. Plate-Cathode Spacing:

(before life) .0406. (after life) .0404. Apparent Density of Coating: (mg. .78.

per 011. mm.). Unit Weight of Coating (mg. per sq. 7.07.

Coating came 011 on exposure to air.

low values of available heater voltage.

alloys X1 to X5 have voltages substantially the same operating characteristics tent in the ternary alloy is increase throughout a protracted life.

By way of contrast and as 1 once is made to Table VII below and to Fig. 23.

l Remainder.

Also as shown in Table VI, with cathode sleeves of these alloys, the oxide coating remained bonded tothe sleeve throughout the cathode'life and with insignificant change of the spacing to the associated anode.

In general, indirectly-heated cathodes made of alloys X1 to X5 exhibit superior emission characteristics and enhanced strength of alloy X previously discussed. By way of specific example, alloyXi strength suitable to pre 1 mil at a pressure of 3750 lb./ sq. inch at temperatures of about 900 C. This alloy and others within the preferred narrow limits of aluminum and tungsten have high strength and low sublimation rate even at above normal operating temperatures. As above pointed out, these alloys have high, stable emission even at subnormal heater voltage (subnormal operating temperature). Thus cath-' odes of these alloys exhibit under widely difierent heater has abet-deflection elude deformation'of more than As shown by the curves and C afford rapid activation of the cathode sleeves, the the maximum attained After less heated cathodes made compare with Figs. 7 I

sion, the emission is very su emission falls quite rapidly from in the first 50 hours of life. of life; the emission of indirectly- Fof these alloys is markedly less to 9 and 22) than the emission maintained by the X to X5 alloys throughout a much longer operating life. It is also to be noted sleeves made of alloys C in heater voltage.

from Table of Fig. 23, although alloys C5 than 200 hours VIII that for cathode 5 and C6, there is poor adherence of the oxide coating to the sleeve and strong pro of early termination of cathode life by flaking or peeling lso to be noted that for these al- 1 short period of high emisbstantially affected by change bability TABLE VIII Characteristics 0; 0

First sign of dome deposit 200 hr none. Type and diameter of deposit heavy, 2 mm none. Activation Rate:

I. at 6.5 v. (Er) 5hr. I. FM 50 hr. Max emission Level and time:

I. at 6.5 v. (Er) 63.6 Ma. (100 hr.) 63.3 Ma. (50 hr.). I. at 4.5 v. (E 60.4 Ma. (50 hr.) 60.7 Ma. (50 hr.). I. FM 16 (50 hr.) 15.9 (50 hr.). D. 0. Life Emiss I. at 6.5 v. (E; 57.2 Ma. ,000 hr.)...- 58.6 Ma. (1.000 hr.). LII. alrtfij v. (Er)... 37.6 (1,000 hr) 388.4 Ma. (1,000 hr.).

5 i O?%1())de Coating Temperature: 7.5 v. 825 0..-- 806 C.

t HQagiZg-Oa(%10)de Leakage:

. v. r 100 V. (Ehk)..- "T Visual Analysis of Diode:

Interface Color- (before life) A L+. (after life) L-- L. Coating Texture.-- Coating Hardness--. S S. Coating Adherence.- Poor Poor. Plate Cathode Spaein (before life) .0403. (after life) coating peeled off. Apparent density of Coating. .79 .79. Unit Weight of Coating 7.72.

From extensive investigation of aluminum-tungstenni-ckel alloys, in part reproduced in the drawings and tables above, it has been determined that the preferred narrow limits of tungsten and aluminum for the sleeves or equivalent base structures of indirectly-heated cathodes are those defined by Table IX below.

TABLE IX Base alloy:

Ni Remainder.

Co- 1% max. Major activating agents:

Al .05 to .10.

W 2.0 to 2.5. Minor activating agents:

M 0.01 to 0.06.

Si .03 max. Residual:

Cu .05 max.

Fe .10 max.

C 0.3 to 0.10.

Mn .05 max.

Ti .01 max.

S .005 max.

Within the narrow limits of tungsten and aluminum of Table IX above, such cathodes exhibit optimum manufacturing, activating, life and operating characteristics A taking into account all of the many factors above discussed.

What is claimed is:

1. A metallic cathode element of the indirectly-heated oxide-coated type characterized by electrical properties of rapid activation, enhanced emission, increased life and permanent low electrical impedance of the bond to the cathode coating and by the mechanical properties of ease of formation by metal-working steps and resistance to deformation when subjected to severe shock, said element being of an alloy containing nickel above about 94%, tungsten in the range of 0.5% to 5%, aluminum in the range of 0.01% to 0.25%, and not significantly in excess of 1% cobalt, 0.15% magnesium, 0.25% silicon, 0.2% copper, 0.2% iron, 0.2% carbon, 0.2%manganese, 0.05% titanium, and 0.01% sulphur.

2. A cathode element as in claim 1 in which the 7 aluminum-tungsten-nickel alloy includes magnesium within the range of from 0.01% to 0.15% as a minor activating agent.

3. A cathode element as in claim 1 in which the aluminum-tungsten-nickel alloy includes silicon within 75 the range of from 0.01% to 0.25 as a minor activating agent.

4. A cathode element as in claim 1 in which the aluminum-tungsten-nickel alloy includes the minor activating agents magnesium and silicon within the combined percentage range of from 0.03% to 0.4% and within the maximum limits of 0.15% magnesium, 0.25% silicon.

5. An indirectly-heated cathode structure characterized by high hot strength and composed of a ternary alloy containing 0.5% to 5% tungsten, 0.01% to 0.25% aluminum and the remainder essentially nickel.

6. An indirectly-heated cathode structure characterized by high hot strength and good thermionic emission properties comprising a cathode base coated with electronemissive material, said base being composed of a ternary alloy containing 0.5% to 5% tungsten, 0.01% to 0.25 aluminum and the remainder essentially nickel.

7. In an electron discharge device, an indirectly-heated hollow cathode structure coated with electron-emissive' material, said structure being composed of a ternary alloy containing 0.5% to 5% tungsten, 0.01% to 0.25 aluminum and the remainder essentially nickel.

8. An indirectly-heated cathode structure characterized by high hot strength and good thermionic-emission properties comprising a cathode base element coated with electron-emissive material, said base being composed of a ternary nickel alloy containing as major activating agents 0.5% to 5% tungsten and 0.01% to 0.25% aluminum, and at least one of the minor activating agents magnesium and silicon within the combined percentage range of from 0.03% to 0.4% and within the maximum limits of 0.15 magnesium, 0.25% silicon.

9. An indirectly-heated cathode structure having the characteristics of rapid activation, high and stable emission over a substantial range of heater voltage, high strength and low sublimation at above normal operating temperatures and composed of a ternary nickel alloy containing aluminum 0.05 to 0.10%, tungsten 2% to 2.5%, and the remainder essentially nickel.

10. An indirectly heated cathode structure as in claim 9 in which the aluminum-tungsten-nickel alloy includes magnesium within the range of from 0.01% to 0.06% as a minor activating agent.

11. A metallic cathode element of the indirectly-heated oxide-coated type characterized by electrical properties of rapid activation, enhanced emission, increased life and permanent low electrical impedance of the bond to the cathode coating and by the mechanical properties of ease of formation by metal-working steps and resistance to deformation when subjected to severe shock, said element of an alloy containing nickel above about 94%, aluminum in the being tungsten in the range of 0.5% to range of 0.01% of 1% cobalt, 0.15% copper, 0.2% iron, 0.2% carbon, titanium, and 0.01% sulphur.

12. A cathode element as in claim 11 in which the aluminum-tungsten-nickel alloy includes magnesium within the range of from 0.01% to 0.15 as a minor activating agent.

13. A cathode element as in claim 11 in which the alurninum-tungsten-uickel alloy includes silicon within the range of from 0.01% to 0.25% as a minor activating agent.

14. A cathode element as in claim ll in which the aluminum-tungsten-nickel alloy includes the minor activating agents magnesium and silicon within the combined percentage range of from 0.03% to 0.04% and within the maximum limits of 0.15% magnesium, 0.25% silicon.

15. An indirectly-heated cathode structure characterized by high hot strength and composed of a ternary alloy containing 0.5% to 5% tungsten, 0.01% to 0.2% aluminum and the remainder essentially nickel.

16, An indirectly-heated cathode structure characterized by high hot strength and good thermionic emission properties comprising a cathode base coated with electron-emissive material, said base being composed of a magnesium, 0.25% silicon, 0.2% 0.2% manganese, 0.05%

to 0.2%, and not significantly in excess I minum,

ternary alloy containing-0.5% to 5% tungsten, 0.01% to 02% aluminum and the remainder essentially nickel.

17. In an electron discharge device, an indirectlyheated hollow. cathode. structure coated with electronemissive material, said structure being composed of a ternary alloy containing 0.5% to 5% tungsten, 0.01% to 0.2% aluminum and-the remainder essentially nickel.

' 18. An indirectlyheated cathode structure characterized by high hot strength and good thermionic-emission properties comprising a cathode base element coated with electron-emissive material, said base being composed of a ternary nickel alloy containing as major activating agents 0.5% to 5% tungsten and 0.01% to 0.2% aluand at least one of the minor activating agents magnesium and silicon within the combined percentage range of from 0.03% to 0.4% and Within the maximum limitsof 0.15% magnesium, 0.25% silicon.

References Gited in' the file ofthis patent UNITED STATES PATENTS 2,103,267 Mandell' Dec. 28, 1937 2,223,862 Widell Dec. 3, 1940 2,323,173 Widen June 29, 1943 2,566,115 Bounds Aug. 28, 1951 FOREIGN PATENTS 11I,841- Australia Apr. 29, 1943 

1. A METALLIC CATHODE ELEMENT OF THE INDIRECTLY-HEATED OXIDE-COATED TYPE CHARATERIZED BY ELECTRICAL PROPERTIES OF RAPID ACTIVATION, ENHANCED EMISSSION, INCREASED LIFE AND PERMANENT LOW ELECTRICAL IMPEDANCE OF THE BOND TO THE CATHODE COATING AND BY THE MECHANICAL PROPERTIES OF EASE OF FORMATION BY METAL-WORKING STEPS AND RESISTANCE TO DEFORMATION WHEN SUBJECTED TO SEVERE SHOCK, SAID ELE- 